Severe Tropical Cyclone Narelle

5 – 15 January 2013 January 2016

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Table of Contents 1 Summary ...... 1 1.1 Intensity analysis ...... 1 1.2 Motion ...... 1 1.3 Structure ...... 2 2 Impact ...... 3 3 Observations ...... 4 4 Forecast Performance ...... 5 TABLE 1. Best track summary for Severe Tropical Cyclone Narelle ...... 6 Figure 1. Best track of Narelle 5-15 January 2013 (times in AWST, UTC+8)...... 9 Figure 2. SSMIS microwave image at 1002 UTC 11 January 2013 around peak intensity...... 10 Figure 3. Comparison of objective and subjective intensity estimates for Narelle...... 11 Figure 4. Comparison of storm surge associated with Narelle...... 12 Figure 5. Accuracy statistics for Narelle ...... 13

1 Summary

A strong monsoon flow combined with a burst of the Madden-Julian Oscillation (MJO) to form a tropical low near 10.5oS 126oE. This tropical low initially moved west southwest and slowly developed. Narelle reached cyclone strength at 0000 Universal Time Coordinated (0800 AWST=UTC+8 hours) 8 January and continued to develop under favourable conditions. From 9 January Narelle tracked in a southwest direction and reached a 10-minute mean wind peak intensity of 105 knots (kn) (195 kilometres per hour (km/h)) at 1200 UTC 11 January when it was located around 470 kilometres (km) to the north northwest of Exmouth, Western Australia (WA). Narelle moved south southwest from 13 January, parallel to the WA coastline, as it weakened due to a combination of increased vertical wind shear and cooler sea surface temperatures (SSTs). Narelle weakened below tropical cyclone strength at 0600 UTC 14 January, finally dissipating well offshore to the west of Perth. Though the tropical cyclone never directly affected the mainland it did cause disruption to Northwest Shelf operations. Narelle also produced a tidal surge which affected the WA coastline from Onslow to Busselton, the peak being 110 centimetres (cm) at Onslow and 84 cm at Exmouth on 13 January, while the surge down the west coast reached 90 cm at Busselton and 78 cm at Fremantle on 16 January. This caused elevated tides that caused some inundation of low lying areas but no major impact overall.

1.1 Intensity analysis A tropical low became evident in an active monsoon trough around 1200 UTC 5 April with an initial Dvorak Data T-number (DT) 1.0. Conditions were favourable for development and the tropical low steadily intensified, reaching tropical cyclone strength at 0000 UTC 8 January. During 8 January curved banding improved and by 9 January an eye pattern emerged. Averaging all objective and subjective intensity guidance Narelle reached a 10-minute mean wind peak intensity of 105 kn (195 km/h) at 1200 UTC 11 January (refer Figure 2). Objective Advanced Dvorak Technique (ADT) failed to analyse an eye pattern so intensity estimates lagged subjective Dvorak estimates until 1200 UTC 11 January (refer Figure 3). During 12 January Narelle began to track south over cooler SSTs and the vertical wind shear increased. This caused Narelle to begin to weaken and as a result the eye pattern disappeared around 1000 UTC 12 January. As Narelle tracked south southwest parallel to the WA coastline it steadily weakened, eventually decreasing to below tropical cyclone strength at 0600 UTC 14 January over ocean to the west of Perth.

1.2 Motion Narelle was steered by the mid-level ridge located over Australia and the tropical cyclone moved west southwest. During 9 January the ridge weakened as a mid-level trough approached from the west and Narelle began to move south southwest. By

0000 UTC 12 January Narelle had been captured by the mid-level trough and was steered south as it weakened under increased vertical wind shear.

1.3 Structure Narelle developed under low to moderate vertical wind shear so the cloud structures were reasonably symmetric until it began to weaken. The tropical cyclone had a larger radius to gales in the southern quadrants for its lifetime. Initially radius to gales ranged from 60 to 90 nm (110 – 167 km), as the tropical cyclone developed this increased to 120 to 150 nm (120 – 278 km). The radius to maximum wind (RMW) was initially 30 nm (56 km), this decreased down to 15 nm (28 km) at peak intensity. The eye diameter ranged in size from 30 nm (56 km) down to around 10 nm (18 km) at peak intensity.

2 Impact

Narelle had no impact on mainland Australia however the Northwest Shelf offshore industries experienced some affects. As Narelle moved parallel to the coast an associated tidal surge was recorded from Onslow around to Busselton, the peak being 110cm at Onslow and 84cm at Exmouth on 13 January (refer Figure 4), while the surge down the west coast reached 90cm at Busselton and 78cm at Fremantle on 16 January. This caused elevated tides that caused some inundation of low lying areas but no major impact overall.

3 Observations

Other than an associated tidal surge there were no observations recorded during the lifetime of Narelle.

4 Forecast Performance

The accuracy statistics obtained by comparing the forecast positions against the best track positions for Narelle are

Forecast 0 06 12 18 24 36 48 72 96 120 144 168 Hour

Absolute 30 46 60 60 65 79 100 144 187 219 182 250 error (km)

RMS error 33 54 72 70 76 90 109 153 217 252 206 277 (km)

Figure 5 is a plot of the accuracy figures for Narelle compared to the five year mean.

TABLE 1. Best track summary for Severe Tropical Cyclone Narelle Refer to the Australian Tropical Cyclone database for complete listing of parameters. AWST is UTC + 8 hours. Please note data between 0600 UTC 4 April and 0600 UTC 6 April from La Reunion RSMC.

Year Month Day Hour Pos. Pos. Po Max Max Cent Rad. of gales Rad. of RMW UTC Lat Long. s. Wind gust . (NE/SE/ storm n mi S E Ac 10 kn Pres SW/NW) (NE/SE/ c. min s. SW/NW) n kn hPa mi

2013 01 05 1200 10.5 126.0 60 20 45 1005

2013 01 05 1800 10.5 125.7 60 20 45 1003

2013 01 06 0000 10.5 125.5 60 25 45 1000

2013 01 06 0600 10.8 125.0 60 25 45 1001

2013 01 06 1200 11.0 123.7 60 25 45 1002

2013 01 06 1800 11.2 122.9 60 25 45 1002

2013 01 07 0000 11.4 121.8 60 25 45 1001

2013 01 07 0600 11.4 121.4 60 25 45 1001

2013 01 07 1200 11.3 120.7 60 25 45 999

2013 01 07 1800 11.6 119.9 45 30 45 997

2013 01 08 0000 11.9 119.1 30 35 50 995 60/90/90/60 30

2013 01 08 0600 12.1 118.4 30 40 55 993 60/90/90/60 30

2013 01 08 1200 12.2 117.8 30 45 65 987 60/90/90/60 30

2013 01 08 1800 12.4 117.2 30 50 70 985 60/90/90/60 30/60/60/30 20

2013 01 09 0000 12.6 116.7 20 55 75 982 60/90/90/60 30/60/60/30 15

Year Month Day Hour Pos. Pos. Po Max Max Cent Rad. of gales Rad. of RMW UTC Lat Long. s. Wind gust . (NE/SE/ storm n mi S E Ac 10 kn Pres SW/NW) (NE/SE/ c. min s. SW/NW) n kn hPa mi

2013 01 09 0600 13.0 116.4 20 60 85 978 75/110/110/75 40/70/70/40 15

2013 01 09 1200 13.4 116.1 20 65 90 972 90/120/120/90 40/70/70/40 15

2013 01 09 1800 13.8 115.9 20 65 90 972 90/120/120/90 40/70/70/40 15

2013 01 10 0000 14.4 115.7 15 70 100 967 90/120/120/90 40/70/70/40 15

2013 01 10 0600 15.6 115.2 15 75 105 964 90/120/120/90 40/70/70/40 15

2013 01 10 1200 16.3 115.0 15 85 120 952 90/120/120/90 50/70/70/50 15

2013 01 10 1800 16.6 114.4 15 90 125 949 90/120/120/90 50/70/70/50 15

2013 01 11 0000 17.0 113.8 15 95 135 943 120/150/150/12 60/80/80/60 15 0

2013 01 11 0600 17.6 113.2 15 100 140 938 120/150/150/12 60/80/80/60 15 0

2013 01 11 1200 17.9 112.7 10 105 145 930 120/150/150/12 60/80/80/60 15 0

2013 01 11 1800 18.3 112.3 10 105 145 930 120/150/150/12 60/80/80/60 15 0

2013 01 12 0000 18.6 112.0 10 105 145 932 120/150/150/12 60/80/80/60 15 0

2013 01 12 0600 19.3 112.0 10 100 140 936 120/150/150/12 60/80/80/60 15 0

2013 01 12 1200 19.9 111.6 10 95 135 941 120/150/150/12 60/80/80/60 15 0

2013 01 12 1800 20.5 111.3 10 85 120 950 110/120/120/90 60/80/60/40 15

Year Month Day Hour Pos. Pos. Po Max Max Cent Rad. of gales Rad. of RMW UTC Lat Long. s. Wind gust . (NE/SE/ storm n mi S E Ac 10 kn Pres SW/NW) (NE/SE/ c. min s. SW/NW) n kn hPa mi

2013 01 13 0000 21.4 110.8 10 70 100 965 90/90/90/60 60/60/30/30 15

2013 01 13 0600 22.3 110.4 10 65 90 969 90/90/110/75 60/60/30/30 20

2013 01 13 1200 23.3 110.1 15 50 70 976 90/90/120/90 60/60/30/30 20

2013 01 13 1800 24.3 110.0 20 45 65 983 60/90/90/60 20

2013 01 14 0000 25.3 109.9 20 40 55 987 60/90/90/60 25

2013 01 14 0600 26.5 109.7 20 35 50 994 0/90/0/0 25

2013 01 14 1200 27.6 109.5 30 25 45 1000

2013 01 14 1800 28.8 109.2 30 25 45 1001

2013 01 15 0000 30.0 109.0 20 20 45 1004

2013 01 15 0600 31.1 109.5 30 15 45 1006

Figure 1. Best track of Narelle 5-15 January 2013 (times in AWST, UTC+8).

Figure 2. SSMIS microwave image at 1002 UTC 11 January 2013 around peak intensity.

(image courtesy of NOAA NRL: http://www.nrlmry.navy.mil/)

Figure 3. Comparison of objective and subjective intensity estimates for Narelle.

Figure 4. Comparison of storm surge associated with Narelle.

Image courtesy of Western Australian Department of Transport http://www.transport.wa.gov.au/imarine/storm-surge- comparison-chart.asp

Figure 5. Accuracy statistics for Narelle